(case involves buyers and processors of farm-raised crawfish suing a pesticide manufacturer under state (LA) product liability law to recover economic loss from decline in farm-raised crawfish allegedly caused by rice seed that was treated with defendant's pesticide; trial court granted summary judgment for defendant and appellate court affirmed; plaintiff did not sustain damages to their person or property and economic loss rule bars recovery in such situations in tort; association between damaged crawfish and economic loss was tenuous because plaintiffs had no actual, enforceable contract right to buy crawfish; LA law does not recognize cause of action for negligent interference with contract rights).